In various industrial fields, such as food, machinery and chemicals, a label on which symbols, letters, patterns, etc., have been printed, i.e., a patterned label, is attached to products or their packaging materials to control the production process. A typical example of such process control is a system utilizing labels on which a bar-code is printed. In a bar-code control system, data such as production conditions, production managers, production period, destination, and product price are read from the bar-code label by a bar-code reader to control production, sales, and distribution.
The bar-code labels that are currently in wide use are made by producing a resin or paper label having poor heat resistance, and then applying an adhesive made of acrylic resin or the like to it. However, because both the label and the adhesive decompose and evaporate at temperatures of 300° C. or higher, they cannot be used in industries requiring high-temperature processing, such as ceramics, metals, and the like. Japanese Patent No. 2614022 discloses heat-resistant labels but does not disclose attaching the labels at such high temperatures. Japanese Unexamined Patent Publication No. 2003-126911 discloses labels to be subjected to a heating process in which an aluminum coil is baked but discloses in Comparative Example 3 in the specification that the information on the label becomes unclear unless the attachment temperature is 150° C. or lower.
Therefore, in the metal mining industry, labels for product management are attached to metal products after the melted and formed metal is cooled to a temperature (generally, near room temperature) in the range in which the labels can be attached. The same applies to the ceramics and glass industries, and other industries requiring high-temperature processing.